Modeling the Effect of Additives on Metal Oxide Chemiresistor Gas Sensors

The additives change the conductance of the metal oxide chemiresistor gas sensor. A model based on the Freundlich adsorption isotherm, giving a power law relation between the electrical conductance of the gas sensor and the concentration of the target gas, describes the steady state response of the metal oxide chemiresistor gas sensor in the best manner. In this paper, the effect of platinum (Pt) and palladium (Pd) on various tin dioxide (SnO
₂
) nanostructures are analyzed and the model parameters are evaluated for the conduction model based on adsorption. The model parameters are fitted using the data extracted from different papers that report the effect of additives to tin dioxide (SnO
₂
) in sensing gases like hydrogen (H
₂
), carbon monoxide (CO), nitric oxide (NO
₂
), or ethanol (C
₂
H
₅
OH). The model parameters are evaluated for the sensing material with and without the additives. The result shows that not only the exponent but also the pre-exponential coefficient, of the power law relation, is changed when doping is done to the sensing material. The major amount of conductance change is observed to be due to the power law exponent when SnO2 with Pt is used for detecting gases like CO, NO
₂
, and H
₂
, etc., while the pre-exponential factor controls conductance change when SnO
₂
with Pd is used in detecting H
₂
. Even though this study is done on SnO
₂
with palladium or platinum, it can be shown that the steady state response of most of the metal oxide chemiresistors with additives can be modeled by the method proposed.